The invention relates to a method and an apparatus for determining the concentration of a gas or a gas component in a gas mixture, by means of the coloration of a reagent test paper.
A variety of measuring devices are known which make use of elongated strips of reagent test paper as the measuring means. In consequence of their simple construction they are very reliable. On account of the extreme measuring sensitivity, they guarantee the accurate determination of for example smoke concentrations or the analysis of gases of such low concentration that measurement by other devices and other methods could be performed only at great expense.
A further use of the known apparatuses is for example the monitoring of a gaseous atmosphere where only the exceeding of a predetermined, for example dangerous, threshold value is to be signalled; so long as the concentration remains below this preselected value, there is no need for an indication, since only the distinction "beneath or above the threshold value" is of interest.
For these and other purposes, the conventional test paper measuring devices have the disadvantage that they continually, i.e., even in "normal conditions", when the gas concentration is beneath the threshold value, steadily consume test paper. These devices operate with continual test paper advancement, either continuously, for example at 1 millimeter per minute, or discontinuously, for example at the rate of one exposure field per gas exposure, i.e., independently of the indicated gas concentration. The result is a considerable consumption of reagent test paper and accordingly considerable operating expense.